Ki Soo Lim

Nanostructure and microripple formation on the surface of sapphire with femtosecond laser pulses

We have demonstrated the creation of polarization-dependent nanogratings with a period of about 250 nm on the surface of sapphire by scanning the femtosecond laser beam with appropriate irradiation conditions. Laser fluence range for nanograting self-formation was very narrow in the slow scan mode. The grating depth variation was observed with atomic force microscope image analysis. To see the composition distribution in the nanostructure, we carried out the Auger signal analysis. In addition, we found a new periodic structure with a period of a few μm and discussed the complex formation mechanism.

Formation of Eu-Doped CaF2 Naonocrystals in Glass-Ceramics by Infrared Laser Irradiation

Glass-ceramic was precipitated on the oxyfluoride glass surface by thermal annealing with a CO2 laser and a heat gun. Micro x-ray diffraction showed the formation of CaF2 ain the exposed region to the laser. Dopant distribution in glass ceramics was probed by confocal fluorescence microscope by observing much strong emission from Eu ions than the glassy area under 405 nm excitation. Much enhanced visible emissions under 365 nm excitation also showed well incorporation of Eu3+ ions into a crystalline environment.

Synthesis and characterization of Sm(DBM)3Phen-and Nd(DBM)3Phen-doped polymethylmethacrylate for potential solar spectrum converter

Sm(DBM)3Phen and Nd(DBM)3Phen were synthesized as stable rare-earth complexes in polymer matrix. Polymethylmethacrylate (PMMA) containing these complexes was highly transparent but exhibited emission peaks in the visible and near-infrared ranges when excited by ultraviolet light. These emission peaks were attributed to energy transfer from excited DBM to rare-earth ions. To evaluate the potential of this material for use in planar solar spectrum converters, complex-doped PMMA layers were solution-casted on top of Si solar cells and their spectral responses were investigated.

Nanograting Fabrication on the Surface of Silicon and Gallium Arsenide Using Femtosecond Laser Pulses

Self-organized nanogratings were formed with a period of sub-wavelength on the surfaces of Si and GaAs wafers by scanning a femtosecond laser beam at 800 nm with appropriate irradiation conditions. The periodicity and shape of the nanogratings formed on the surfaces of two semiconductors were studied with different laser polarizations and various scan speeds. We also studied the profile and variation of the nanograting depth from the surface by atomic force microscope (AFM) analysis, and merged neighboring nanogratings to form a large area of grating structure.

Three-Dimensional Optical Bit Memory in Sm(DBM)3Phen-Doped and Un-Doped Poly(methyl methacrylate)

The feasibility of three-dimensional optical bit memory is demonstrated by using the change of fluorescence and refractive index in Sm(DBM)3Phen-doped and un-doped Poly(methyl methacrylate). After a femtosecond pulsed laser irradiation, a refractive-index bit and a fluorescent bit can be formed at the same position inside the bulk sample. Multilayer patterns recorded by tightly focusing the pulsed laser beam were read out by a reflection-type fluorescent confocal microscope, which can detect the reflection signal and also the fluorescent signal of the stored bits. The signal-to-noise ratio via the two retrieval modes was compared as a function of recording depth. The stored bits were retrieved with a high signal-to-noise ratio in the absence of any crosstalk and the detection of the fluorescent signal enables retrieval of the stored bits with a higher S/N ratio.